A DOMAIN OF MURINE RETROVIRUS SURFACE PROTEIN GP70 MEDIATES CELL-FUSION, AS SHOWN IN A NOVEL SC-1 CELL-FUSION SYSTEM

Virus-induced cell fusion of the fusion-from-without type was observed in SC-1 cells infected with Moloney murine leukemia virus when grown in NIH 3T3 cells. Replication-competent virus mutants with altered surface protein gp70 were examined. Fusion mutations were found in the proline-rich region of gp70. They acted on a step after binding and before or during endocytosis. The fusion mutants had an altered gp70 isomer pattern, presumably caused by different glycosylation. Other mutants with deleted glycans were analyzed, add some which also showed defective fusion were found. The interrelationship of the proline-rich region, glycosylation, and fusion is discussed.